The present invention relates in general to electric power supplies and more particularly power converters; more specifically still, it relates to an interface and controller for selectively and/or adaptively changing the magnitude of converter output voltage.
Power converters for converting AC power to a regulated DC level are well-known and widely used in a variety of applications, one important such application being recreational vehicles (e.g., boats, motorhomes, etc.). Low-cost power converters typically comprise a rectifier and DC voltage regulator which controls the output voltage to be near some pre-determined level under optimum or standard operating conditions. However, the output voltages of these power converters is subject to substantial variation and instability which limits their success as well as their range of applications. Accordingly, relatively costly DC motors, which operate properly with a power supply which is not stable, must sometimes be used in recreational vehicles if low-cost DC voltage regulators are employed and an even more significant adverse effect is the overall battery-charging performance and characteristics of such systems, which often overcharge and/or undercharge, thereby shortening operating life and causing defective performance.
An alternative to such DC voltage regulators are switched power converters. Switched power converters have a more stable output voltage but the switching power circuitry required to produce the more stable output voltage is costly. In addition, even these more expensive converters do not necessarily provide the most optimum battery-charging and often do not maintain performance since their outputs are not adaptive to changing conditions and therefore sometimes exceed or fail to meet particular requirements and conditions encountered. For instance, a 13.6 volt battery charge level may at times be too high and damage the battery while at other times it will be insufficient to charge a battery as rapidly as desired. Therefore, a need has arisen for power converters capable of outputting various voltages, and a means for controlling these operating voltages in accordance with actual conditions encountered.
Having the capability of operating over a range of voltages is desirable because, at certain times, the user will need to charge the battery faster. Increasing output voltage will prevent electrolyte stratification and reduce sulfation, thus extending both the life and capacity of the battery. In addition, increasing output voltage will improve performance of load items such as power slide-outs. On the other hand, decreasing converter output voltage slightly will reduce water boil-off in the battery and, therefore, limit maintenance and extend operating life. Further, decreasing output voltage will reduce the current that the converter draws from the AC line. This will help keep the load current of the main RV power cord below its maximum capacity when other loads, such as an air conditioner, turn on.
The problem with respect to the draw on the load current is that it has steadily increased as more and more loads (such as power slide-outs) are added to these vehicles. As a result, higher capacity converters have become necessary. Now, at full power, the converter itself draws 11 to 12 amps and although most load devices are wired for 30-amp service, the newer bus-type vehicles require 50-amp service. Therefore, some converter designs try to deal with this problem by using circuitry which limits their allowable draw on load current, while others turn the converter off when the battery is at least minimally charged and then later turn the converter back on. However, this obviously provides unsatisfactory overall performance and is not likely to properly charge and maintain the associated vehicle/coach batteries. Therefore, some converters have now been designed to effectively turn off under certain conditions by reducing their output voltage to a very low level. In one such design, the converter has a dual-voltage terminal such that if the two contacts on the terminal are shorted, the output goes to a predetermined maximum level and, if left open, the output goes to a predetermined minimum level. This design contains a toggle switch which allows the user to manually control the high and low output level as desired. In another embodiment of this system, an electronic module attached to the converter reads the battery voltage and automatically responds by signaling the converter to increase or decrease the charging voltage. For example, if it has been "high" for a predetermined time, the output voltage will automatically drop to the lower voltage.
Overall, the functions of such a device are limited. For instance, in the former embodiment, if the user toggles the switch "high" and forgets, he could burn up his battery because the design lacks a safety feature. Furthermore, this device is built directly into the converter, making the converter itself more expensive. In addition, the particular levels are set by the factory, and only two specific values are available to the user. Consequently, there is no real versatility to the design, and no way for the user to readily or conveniently select an output level different than those built-in at the factory. Further, in the latter embodiment, the device does not allow for manual control by switching between high and low voltage levels. Another problem with this embodiment is that the external module cannot be utilized with older models of the converter unless the converter is retrofitted with a dual-voltage terminal.